That's odd, if you haven't done anything to change them like that.
First, go to Start and right-click on Computer (on the right side of the menu) and select Properties. On the left hand side of the window that opens up, click Advanced system settings. In that window, (in the Advanced tab, but it should automatically open to that tab) click on Settings under the Performance header. Make sure the "Let windows decide what's best for my computer" button is checked. If it already is, try just restarting your computer. If neither of those help, let me know.